TX Power on alarm

Some time ago I ask about the "timer on" alert timer and that I frequently walked away form my TX (12S) and left its power on (while building and after tweaking, etc.).

My 12S makes a very quiet jingle of sorts but if I am more than 24-36" inches from the TX, this sound can not be heard.

But two nights ago, it sounded loud and clear. It has done it a couple of time not never consistently or reliable. I am wondering if this is an issue with my 12S please? How does your 12S sound? What is normal?